LABORATORY AND POND EVIDENCE FOR SHRIMP (Penaeus stylirostris) PREDATION BY DAMSELFLY NYMPHS (Ischnura rarnburi)

A negative relationship was found between damselfly nymph population density and final shrimp population density in ponds. The importance of damselfly nymphs as potential predators of post-larval shrimp and the effect of shrimp size, salinity, and substrate type on this predatory relationship were evaluated by a series of laboratory experiments. When 5–10 nymphs and 15 post-larval shrimp were stocked in tanks with a 0.96 m2 bottom area and containing 150 liters of water, each nymph averaged killing 1.7 shrimp per day at 10 ppt salinity and 0.6 shrimp per day at 20 ppt. Damselfly predation rates were inversely related to the three shrimp sizes (average 8.55, 12.89, and 17.30 mm). Presence or absence of a natural muddy substrate had no effect on shrimp mortality caused by nymphs. The results of these experiments strongly suggest that predation of damselfly nymphs on post-larval shrimp, when they occur together in ponds, may be a serious problem for the culturist.